diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index a0fcd717f..f07472b33 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -2715,6 +2715,7 @@ ngx_http_send_special(ngx_http_request_t *r, ngx_uint_t flags)
             b->last_buf = 1;
 
         } else {
+            b->sync = 1;
             b->last_in_chain = 1;
         }
     }